1. Field of the Invention
The present invention relates to an apparatus and method for realizing an all-optical NOR logic device. Specially it relates to an all-optical NOR logic device among all-optical logic devices, in which a signal transmitted from a given point of an optical circuit such as an optical computing circuit is used as a pump signal and a probe signal.
2. Description of the Related Art
Future data communication networks are expected to be used for multimedia services associated with audio signals, still images, and moving images. For this reason, it is expected that the processing capacity of a basic network including a local area network (LAN) and a backbone will be increased up to a range from several hundred Gbit/s to several Tbit/s in future.
As important techniques for transmitting, processing and exchanging data of such a high capacity in a high speed, an optical signal processing technique has been proposed.
In particular, an all-optical logic operation is necessary for optical signal processing systems to avoid a cumbersome electro-optic conversion. All-optical logic devices, which conduct the above mentioned all-optical logic operation, are used for high-speed and parallel processing of data.
Such all-optical logic devices are important in association with next-generation optical computers and all-optical signal processing. For this reason, recently active research and development are being made.
In particular, it is expected that nonlinear effects of semiconductor optical amplifiers will be eventually used to realize all-optical switches or logic devices for optical computers in future.
All-optical logic devices using nonlinear gains of semiconductor optical amplifiers have been implemented using a single-arm ultrafast nonlinear interferometer (N. S. Patel, et al., Opt. Lett., 21, 1446 (1996)) and directly modulated two pump beam switching experiments with the same pump wavelength (T. Houbavlis, et al., IEEE Photon. Technol. Lett., 11, 334 (1999)). However, there has been a limitation in realizing desired logic operations using optical signals of a given wavelength transmitted from the output end of a complex optical circuit.
Therefore, an object of the invention is to solve the above mentioned problems while generalizing a realization of all-optical logic devices, and to provide an apparatus and method for realizing an all-optical NOR logic device, which is modulating two pump signals using an external modulation scheme, thereby allowing a signal transmitted from a given point of an optical circuit to be used as a pump signal, while being capable of optical signals of two different wavelengths, thereby allowing optical signals of a given wavelength transmitted from a given point of the optical circuit to be used as pump signals.
In accordance with one aspect, the present invention provides an apparatus for realizing an all-optical NOR logic device comprising: pump signal generating means for generating two pump signals of different wavelengths; external modulation means for modulating the generated pump signals; delay/control means including delay means adapted to delay a pump signal, splitted from the modulated pump signals, traveling along an optical path, and control means adapted to control the other pump signal, splitted from the modulated pump signals, traveling along another optical path, to have the same polarization and intensity as those of the pump signal passing through the delay means; amplification means for amplifying the sum of the pump signals respectively outputted from the delay means and the control means so that the amplified pump signal sum saturates a semiconductor optical amplifier; the semiconductor optical amplifier exhibiting gain saturation and wavelength conversion characteristics in response to an output signal from the amplification means, indicative of the amplified pump signal sum, and a probe signal passing therethrough; and coupling/splitting means coupled to respective output ends of the pump signal generating means, the external modulation means, the delay/control means, and the amplification means, and adapted to conduct coupling and splitting operations for pump signals.
In accordance with another aspect, the present invention provides a method for realizing an all-optical NOR logic device wherein two pump signals of different wavelengths pass through a semiconductor optical amplifier, along with a probe signal, in a state in which the pump signals totally have an intensity capable of saturating the semiconductor optical amplifier, to allow the semiconductor optical amplifier to exhibit gain saturation and wavelength conversion characteristics, whereby an all-optical NOR logic operation is realized.